This project is aimed at understanding the molecular mechanism(s) of sex-dependent gene regulation of steroid hydroxylases in liver and renal microsomes from mice. Genetic regulation: We defined two loci (Rip and Rsh) which regulate female-specific expression of "I"-P-450, 16Alpha (an isozyme of testosterone 16Alpha-hydroxylase) in liver microsomes and expression of P-450, 15Alpha (an isozyme of testosterone 15Alpha-hydroxylase) in renal microsomes, respectively. With inbred strain (9XA), the Rip locus was located on mouse chromosome 7. The two loci are expected to be transacting genetic elements whose gene products are not yet identified. Hormonal regulation: Growth hormone (GH) is a masculinizing factor which acts by expressing the male-specific isozyme of testosterone 16Alpha-hydroxylase ("C"-P-450, 16Alpha) and representing female-specific hydroxylases ("I"-P-450, 16Alpha and P-459, 15Alpha) in male liver. Estrogen is another repressor of "I"-P-450, 16Alpha in male liver and estrogen-dependent repression is under control of either the Rip locus or a locus closely linked to the Rip locus. Expression of P-450, 15Alpha is growth hormone- and androgen-dependent in mouse kidney. It was also found that the induction of "I"-P-450, 16Alpha by phenobarbital in 129/J mice is due to a derepression, presumably through an interaction with pathway of the hormonal repression of this gene. Cloning and characterization of cDNAs and genomic DNAs: Four different cDNAs for the "I"-P-450, 16Alpha family were isolated and DNA sequence data revealed that three of these cDNAs represent "I"-P-450, 16Alpha mRNAs derived from a single gene by an alternative splicing and utilization of poly A sites. One other cDNA shared 90% DNA sequence homology with "I"-P-450, 16Alpha, 1481bp of "C"-P-450, 16Alpha cDNA were sequenced and the amino acid sequence was deduced from it. "C"-P-450, 16Alpha had only 20% sequence homology with other known P-450s. The "C"-P-450, 16Alpha gene family is on mouse chromosome 15. Two closely related P-450, 15Alpha cDNAs were sequenced (98% homology) and two tandomly repeated P-450, 15Alpha genes were found on mouse chromosome 7.